Shielded probe apparatus for probing semiconductor wafer

ABSTRACT

A shielded probe apparatus is provided with a shielded probe and a tri-axial cable that are electrically connected within a shielded chassis. The shielded probe apparatus is capable of electrically testing a semiconductor device at a sub 100 fA operating current and an operating temperature up to 300 C.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a Divisional of U.S. patent application Ser. No. 11/270,044,filed Nov. 9, 2005, now U.S. Pat. No. 7,259,577 which is a Continuationapplication of U.S. patent application Ser. No. 10/607,768, filed Jun.27, 2003 now U.S. Pat. No. 6,992,495 which claims priority to U.S.patent application Ser. No. 60/392,394, filed Jun. 28, 2002, thecontents of which are incorporated herein in their entirety byreference.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor test equipment,and more particularly, to a shielded probe used in semiconductor testequipment for electrically probing devices on a semiconductor wafer.

BACKGROUND OF THE INVENTION

The semiconductor industry has a need to access many electronic deviceson a semiconductor wafer. As the semiconductor industry grows anddevices become more complex, many electrical devices, most commonlysemiconductor devices, must be electrically tested, for example, forleakage currents and extremely low operating currents. These currentsare often below 100 fA. In addition, the currents and devicecharacteristics are often required to be evaluated over a widetemperature range to understand how temperature affects a device. Toeffectively measure at currents below 100 fA, a measurement signal mustbe isolated from external electrical interference, leakage currentsthrough the dielectric material, parasitic capacitance, triboelectricnoise, piezoelectric noise, and dielectric absorption, etc.

At present, semiconductor test equipment has been designed to try toprevent the above described interference or noise, etc. at a testequipment side, by driving a guard layer of a tri-axial cable at thesame potential as a center signal conductor of the tri-axial cable. Theouter shield of the tri-axial cable is grounded to the test equipment.It is desired that external electrical interference, leakage currentsthrough the dielectric material, parasitic capacitance, triboelectricnoise, piezoelectric noise, and dielectric absorption are significantlyreduced or eliminated.

Also, because of the materials characteristics of dielectrics, it isoften difficult to test characteristics of semiconductor devices in awide operating temperature range.

Accordingly, there is a need for improved semiconductor test equipmentfor electrically probing semiconductor devices at low currents and overa wide temperature range.

SUMMARY OF THE INVENTION

To solve the above and the other problems, the present inventionprovides a shielded probe apparatus connected to semiconductor testequipment wherein the shielded probe apparatus includes a shielded probeand a tri-axial cable. The shielded probe includes a probe pin typicallya metal wire made of electrochemically etched tungsten or the like. Theprobe pin is shielded and configured to electrically connect to thetri-axial cable for electrically probing semiconductor devices at lowcurrents and over a wide operating temperature range.

In one embodiment, the shielded probe apparatus is capable ofelectrically testing a semiconductor device at a sub 100 fA operatingcurrent and an operating temperature up to 300 C.

In one embodiment, the tri-axial cable is connected to the shieldedprobe within a shielded chassis. The shielded probe includes a probe pinsurrounded by a dielectric layer, an electrically conductive guardlayer, and an optional protective dielectric layer. The tri-axial cableincludes a center signal conductor surrounded by a dielectric layer, aconductive coating to reduce triboelectric effects, a conductive guardlayer, a second dielectric layer, a conductive shield layer, and aprotective cover. The tri-axial cable is connected to the shielded probeby electrically connecting the center signal conductor to the probe pin,such as by using high temperature to solder/braze or crimp the probe pinon the center signal conductor and in a preferred embodiment,shrink-tube, crimp, or clamp the tri-axial cable and the shielded probeto electrically connect the guard layer of the tri-axial cable to theconductive guard layer of the shielded probe. It will be appreciatedthat other suitable means of electrically connecting the center signalconductor and the probe pin and electrically connecting the guard layerof the tri-axial cable and the conductive guard layer of the shieldedprobe can be used without departing the scope of the principles of theinvention.

Accordingly, the dielectric layer, the conductive guard layer, and theoptional second dielectric layer of the shielded probe significantlyreduce external electrical interference and allow the probe pin to testand measure small currents, such as below 100 fA. Also, the shieldedprobe is allowed to test the characteristics of the semiconductordevices not only in a low operating temperature but also in a highoperating temperature, i.e. a wide operating temperature range by usingflexible dielectric materials compatible with high temperatures. Inaddition, the connection between the guard layer of the tri-axial cableand the conductive guard layer of the shielded probe and the connectionbetween the center signal conductor and the probe pin help preventleakage currents through the dielectric materials, parasiticcapacitance, piezoelectric noise, and dielectric absorption. Further,the conductive coating between the dielectric layer and the guard layerof the tri-axial cable significantly reduces and/or eliminatestriboelectric noise.

These and other features and advantages of the present invention willbecome apparent to those skilled in the art from the following detaileddescription, wherein it is shown and described illustrative embodimentsof the invention, including best modes contemplated for carrying out theinvention. As it will be realized, the invention is capable ofmodifications in various obvious aspects, all without departing from thespirit and scope of the present invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of a typicaltri-axial cable used in semiconductor test equipment.

FIG. 2A is one embodiment of a shielded probe in accordance with theprinciples of the present invention.

FIG. 2B is a cross-sectional view of one embodiment of the shieldedprobe, as shown in FIG. 2A, in accordance with the principles of thepresent invention.

FIG. 3 is a schematic view of one embodiment of a shielded probeapparatus used in semiconductor test equipment, in accordance with theprinciples of the present invention.

FIG. 4A is a cross-sectional view of one embodiment of a tri-axial cableof the shielded probe apparatus, along line 4A-4A in FIG. 3, inaccordance with the principles of the present invention.

FIG. 4B is a cross-sectional view of one embodiment of the tri-axialcable of the shielded probe apparatus, along line 4B-4B in FIG. 3, inaccordance with the principles of the present invention.

FIG. 4C is a cross-sectional view of one embodiment of the tri-axialcable connected to the shielded probe of the shielded probe apparatus,along line 4C-4C in FIG. 3, in accordance with the principles of thepresent invention.

FIG. 5 is a side cross-sectional view of one embodiment of the tri-axialcable connected to the shielded probe of the shielded probe apparatus,in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of a preferred embodiment, reference ismade to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

For purposes of explanation, numerous specific details are set forth inthe following description in order to provide a thorough understandingof the present invention. However, it will be evident to one of ordinaryskill in the art that the present invention may be practiced withoutsome of these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order tofacilitate description.

The present invention utilizes the center signal conductor, guard layer,and ground of a tri-axial cable provided by semiconductor test equipmentor tester to electrically isolate a probe pin enabling the low currentmeasurements, for example, sub 100 fA measurements. The presentinvention also allows the tester to electrically probe devices over awide operating temperature range, not only at a low operatingtemperature but also a high operating temperature, e.g. an operatingtemperature up to 300 C.

FIG. 1 illustrates a cross-sectional view of a typical tri-axial cable100 with a center signal conductor 102 surrounded by a first dielectriclayer 104. The first dielectric layer 104 is surrounded by a guard layer106. The guard layer 106 is electrically conductive and is surrounded bya second dielectric layer 108. A conductive coating or dispersion layer107 is sandwiched between the first dielectric layer 104 and the guardlayer 106. The tri-axial cable 100 also includes a shield layer 110 anda protective dielectric cover layer 111 to isolate the tri-axial cablefrom external interference or other environmental hazard.

It will be appreciated that the term “surrounded” used herein andhereinafter is not limited to describe one layer being surrounded byanother layer in its entirety. In some embodiments, one layer may bepartially surrounded by another layer, whereas in other embodiments, onelayer may be entirely surrounded by another layer.

FIGS. 2A and 2B illustrate a shielded probe 112 which includes a probepin 114. The configuration of the probe pin 114 can be varied, a coupleof which are disclosed in a pending utility patent application, Ser. No.09/730,130, filed on Dec. 4, 2000, which is a Continuation-In-Part (CIP)patent application of Ser. No. 09/021,631, filed on Feb. 10, 1998, whichare incorporated herewith by references.

The probe pin 114 is surrounded by a first dielectric layer 116preferably made of a thin, flexible high temperature dielectricmaterial, such as poly (tetrafluoro-p-xylylene), a class of polymersknown as parylene. The first dielectric layer 116 is preferably coatedon the probe pin by a physical or chemical-vapor deposit (PVD or CVD)method. It will be appreciated that other suitable flexible hightemperature dielectric materials, such as epoxies, or other suitablecoating methods can be used within the scope of the present invention.

The probe pin 114 with the dielectric layer 116 is preferablysputter-coated with an electrically conductive guard layer 118. Theconductive guard layer 118 is preferably made of gold. It will beappreciated that other suitable conductive coating materials and coatingmethods can be used without departing from the scope of the presentinvention.

A second dielectric layer 122 may be provided outside of the conductiveguard layer 118. The second dielectric layer 122 is an optionalprotective coating which provides protection layer for the conductiveguard layer 118. The second dielectric layer 122 is preferably made of athin, flexible high temperature dielectric material, such as polyamide.It will be appreciated that other suitable flexible high temperaturedielectric materials can be used within the scope of the presentinvention.

As shown in FIG. 3, a shielded probe apparatus 124, in accordance withthe principles of the present invention, includes an electricallyshielded chassis 126 and a ceramic assembly 128 for electrically probingsemiconductor devices (not shown). A tri-axial cable 130 ofsemiconductor test equipment is inserted into the shielded chassis 126at one end 132 and connected to the shielded probe 112 at the other end134.

As shown in FIG. 4A, the tri-axial cable 130 includes a center signalconductor 136 on which testing signals are carried from the testequipment to the shielded probe 112. The center signal conductor 136 issurrounded by a first dielectric layer 138 preferably made of hightemperature PTFE (Teflon). The first dielectric layer 138 is surroundedby an electrically conductive coating or dispersion layer 140. Theconductive coating or dispersion layer 140 is sandwiched between thefirst dielectric layer 138 and an electrically conductive guard layer142 to reduce triboelectric effects. In a testing operation, the guardlayer 142 is driven at the same potential as the center signal conductor136 such that the capacitance between the guard layer 142 and the centersignal conductor 136 is eliminated. Accordingly, the parasiticcapacitance is eliminated, and current leakage is prevented.

An optional second dielectric layer 144 may be provided outside of theguard layer 142. A shield 146 and a protective dielectric cover (notshown) are provided outside of the guard layer 142 and/or the optionalsecond dielectric layer 144 to isolate the tri-axial cable 130 fromexternal interference.

As shown in FIG. 3, the tri-axial cable 130 is inserted into the chassis126 where the shield 146 and the protective dielectric cover (not shown)of the tri-axial cable 130 are stripped away and electrically connectedto the ground. FIG. 4B illustrates a cross-sectional view of the cable130 along line 4B-4B in FIG. 3. The optional second dielectric layer 144may extend to the shielded probe 112 or terminate at the chassis'sidewalls.

FIG. 4C illustrates a cross-sectional view (along line 4C-4C in FIG. 3)where the tri-axial cable 130 is connected to the shielded probe 112.FIG. 5 illustrates a side cross-sectional view of one embodiment of thetri-axial cable 130 connected to the shielded probe 112 of the shieldedprobe apparatus 124. The tri-axial cable 130 is attached to the shieldedprobe 112, preferably by using high temperature to solder/braze or crimpthe probe pin 114 on the center signal conductor 136, and shrink-tube,crimp, or clamp the tri-axial cable 130 and the shielded probe 112 intoa shrink tube layer 148 to electrically connect the probe pin 114 to thecenter signal conductor 136. A second shrink tube layer 149 electricallyconnects the guard layer 142 of the tri-axial cable 130 to theconductive guard layer 118 of the shielded probe 112. It will beappreciated that other suitable means of electrically connecting thecenter signal conductor and the probe pin and electrically connectingthe guard layer of the tri-axial cable and the conductive guard layer ofthe shielded probe can be used without departing the scope of theprinciples of the invention.

In one embodiment, the optional second dielectric layer 144 of thetri-axial cable 130 and/or the optional second dielectric layer 122 ofthe shielded probe may be shrink-tubed by folding back and over (notshown) the tri-axial cable 130 and the shielded probe 112, respectively,so as to help retain the physical connection between the shielded probe112 and the tri-axial cable 130.

Further referring to FIG. 3, a probing end of the shielded probe 112 isinserted into a hole and a slot of the high temperature ceramic assembly128 or other suitable high temperature-resistant material, as describedin the pending utility patent application, Ser. No. 09/730,130, filed onDec. 4, 2000, which is a Continuation-In-Part (CIP) patent applicationof Ser. No. 09/021,631, filed on Feb. 10, 1998, which are incorporatedherewith by references.

Further in one embodiment, the probe pin 114 is made ofelectrochemically etched tungsten or other suitable materials. Thediameter of the probe pin 114 is preferably in a range of 0.1 mm to 0.25mm. It will be appreciated that the materials, diameter, andconfiguration of the probe pin 114 can be varied without departing fromthe principles of the present invention.

From the above description and drawings, it will be understood by thoseof ordinary skill in the art that the particular embodiments shown anddescribed are for purposes of illustration only and are not intended tolimit the scope of the present invention. Those of ordinary skill in theart will recognize that the present invention may be embodied in otherspecific forms without departing from its spirit or essentialcharacteristics. References to details of particular embodiments are notintended to limit the scope of the invention.

1. A shielded probe apparatus, capable of electrically testing asemiconductor device at a sub 100 fA operating current and an operatingtemperature up to 300 C., comprising a shielded probe and a tri-axialcable that are electrically connected within a shielded chassis, whereinthe shielded probe comprises: a probe pin; a first dielectric layer, theprobe pin being surrounded by the first dielectric layer; a conductiveguard layer, the first dielectric layer being surrounded by theconductive guard layer; and a second dielectric layer, the conductiveguard layer being surrounded by the second dielectric layer.
 2. Theapparatus of 1, wherein the tri-axial cable comprises: a center signalconductor; a first dielectric layer, the center signal conductor beingsurrounded by the first dielectric layer; a conductive layer, thedielectric layer being surrounded by the conductive layer; a guardlayer, the conductive layer being surrounded by the guard layer; asecond dielectric layer, the guard layer being surrounded by the seconddielectric layer; a shield, the second dielectric layer being surroundedby the shield; and a protective cover, the shield being surrounded bythe protective cover.
 3. The apparatus of claim 2, wherein the probe pinand the center signal conductor are electrically connected to eachother.
 4. The apparatus of claim 3, wherein the probe pin iselectrically connected to the center signal conductor.
 5. The apparatusof claim 3, further comprising a shrink tube to shrink-tube the probepin and the center signal conductor.
 6. The apparatus of claim 2,wherein the conductive guard layer of the shielded probe and the guardlayer of the tri-axial cable are electrically connected to each other.7. The apparatus of claim 6, further comprising a second shrink tube toshrink-tube the conductive guard layer and the guard layer.
 8. Theapparatus of claim 2, wherein the guard layer of the tri-axial cable isdriven to the same potential as the center signal conductor, and theshield of the tri-axial cable is grounded to the shielded chassis.
 9. Ashielded probe apparatus, capable of electrically testing asemiconductor device at a sub 100 fA operating current and an operatingtemperature up to 300 C., comprising a shielded probe and a tri-axialcable that are electrically connected within a shielded chassis, whereinthe shielded probe comprises: a probe pin; a dielectric layer, the probepin being surrounded by the dielectric layer; a conductive guard layer,the dielectric layer being surrounded by the conductive guard layer;wherein the tri-axial cable comprises: a center signal conductor; afirst dielectric layer, the center signal conductor being surrounded bythe first dielectric layer; a conductive layer, the dielectric layerbeing surrounded by the conductive layer; a guard layer, the conductivelayer being surrounded by the guard layer; a second dielectric layer,the guard layer being surrounded by the second dielectric layer; ashield, the second dielectric layer being surrounded by the shield; anda protective cover, the shield being surrounded by the protective cover;and wherein the conductive guard layer of the shielded probe and theguard layer of the tri-axial cable are electrically connected to eachother.
 10. The apparatus of claim 9, further comprising a second shrinktube to shrink-tube the conductive guard layer and the guard layer. 11.The apparatus of claim 9, wherein the guard layer of the tri-axial cableis driven to the same potential as the center signal conductor, and theshield of the tri-axial cable is grounded to the shielded chassis.